1. Field of the Invention
The present invention relates to an image-reading device, and particularly to an image-reading device employing a contact image sensor (CIS) having a plurality of image sensor integrated circuits (IC) chips arranged linearly.
2. Description of Related Art
Recently, time period of clock signal is used at a boundary speed at which an image sensor can read an image. One conventional image-reading device disclosed in Japanese unexamined patent application publication No. 2003-298813 includes a contact image sensor having a plurality of image sensor IC chips arranged linearly and divided into blocks of a natural multiple of three. Each block outputs an image signal to a triple-channel analog front end (AFE), thereby improving the speed for reading image signals. The triple-channel AFE is widely used in image-reading devices because, along with single-channel AFEs, triple-channel AFEs are more popular than AFEs having another number of channels and are mass-produced and, therefore, less expensive.
Another conventional image-reading device disclosed in Japanese unexamined patent application publication No. HEI-7-236026 is provided with a plurality of multiplexers. The image-reading device can increase the speed for outputting data in proportion to the number of the multiplexers by outputting the data from the plurality of multiplexers.
The conventional image-reading device disclosed in Japanese unexamined patent application publication No. 2003-298813 is problematic in that when the image reading area increases, the number of blocks of image sensor IC chips into which the contact image sensor is divided will likely increase, thereby requiring a plurality of triple-channel AFEs. When using contact image sensors for an A3-size original, for example, the contact image sensor is divided into six blocks of image sensor IC ships, thereby requiring two triple-channel AFEs.
In addition, a sampling period among a single pixel reading period in which the image sensor IC ship can samples an image is one part of the single pixel reading period. Therefore, the image-reading device disclosed in Japanese unexamined patent application publication No. HEI-7-236026 is problematic in that a non-sampling period among a single pixel reading period that is not used for sampling prevents the speed for outputting data from increasing.